Vibration actuators are built into mobile electronic devices, and are broadly used as devices to communicate to the user, through a vibration, that there is an incoming call, or that a signal, or the like, such as an alarm, has been generated, and have become indispensable devices in wearable devices, which are carried on the body of the user. Moreover, in recent years vibration actuators have been of interest as devices by which to achieve haptics (skin-sensed feedback) in the human interfaces such as touch panels.
In a vibration actuator, a movable element that is equipped with a weight and a spring is supported on a stationary element so as to enable vibration, where a coil or a magnet is attached to the movable element side, and the other is attached to the stationary element side, and a driving signal (a driving pulse) of the resonant frequency (the natural frequency) that is determined by the weight and the spring is applied to the coil to cause the movable element to vibrate at a large amplitude.
Moreover, in the prior art, as disclosed in Japanese Unexamined Patent Application Publication 2017-77153, a magnetic field having viscosity is filled into a gap that is open between the coil that is provided in the stationary element and the magnet that is provided in the movable element, to cause the magnetic fluid to function as a damper at the time of vibration of the movable element.